This invention relates to process and apparatus for forming containers from extruded sheet thermoplastic material with the utilization of plug-assisted pressure and/or vacuum forming techniques. It is known in the art to form tub-like containers by continuous rotary means from sheet stock such as shown in U.S. Pat. No. 3,027,596. The instant invention likewise provides thermoforming apparatus that rotates about a horizontal axis but, unlike the previously mentioned patent, performs thermoforming on vertically extruded thermoplastic material in a vertical plane between opposed rotating discs. Product uniformity has been made possible by the utilization of a wedge-shaped thermoplastic feedstock to compensate for the variation in tangential speed of the material being processed. U.S. Pat. Nos. 3,181,202, 3,518,725 and 3,771,938 illustrate rotary drum thermoforming wherein flat feedstock is fed to the surface of a rotating thermoforming drum. The instant invention differs from all of the above-mentioned patents in that molten sheet is extruded downwardly in the vertical direction between substantially parallel plates parallel to their plane of rotation and normal to their axis of rotation. Further, the instant invention does not use preformed sheet, which is reheated and fed horizontally onto the surface of a thermoforming drum as shown in the above-mentioned references. U.S. Pat. Nos. 3,578,735 and 3,600,753 illustrate flat bed plug-assisted thermoforming apparatus. These types of devices likewise require horizontal sheet stock and when used with such materials as polypropylene, which is highly plastic at thermoforming temperatures, require special devices to tenter the material and prevent it from stretching before thermoforming. The instant invention avoids material handling problems encountered in all of the above-mentioned patents by extruding a sheet of material vertically downwardly between vertical discs which rotate about a horizontal axis. By this means, the effect of gravity on the material is utilized beneficially rather than creating a problem that must be compensated for. Because the tangential speed of any point on the disc varies from the center of rotation to the extreme periphery of the forming discs, the sheet of material that is extruded is wedge-shaped in cross-section.